Why the Angle Top Trunk?

I've always been intrigued by the design of the lid with trunks like these. Maybe the builder angled the top to give it more strength, which could make sense. Deeper interior lid storage for a compartment? Doesn't matter , I guess. I've been wanting to work on one for a while and when I found this one, it was rusted solid, pretty much. I also liked the design of the embossed metal which has a 'swirl' pattern rather than a floral, or crocodile imprint. So it's the wire wheel on the drill routine for days to get it clean, followed by lots of steel wool and then clear coating. Maybe 10 or 12 coats on the slats to jazz it up and then a cotton drill fabric for lining, with a few strands of piping around the edges. The final result reminds me of a castle, in a way, and that makes as much sense as, the angled top.